simple method Download DooMLoRD_v1_Xperia-2011-ICS-ROOT-emu-busybox-su.rar
Enable UNKNOWN SOURCES and Connect your a13 tab in USB DEBUGGING mode, then run runme.bat file from the package.
sit back read the on screen instructions
the device will reboot a couple of times
when the script finishes it will say "ALL DONE" Your tablet is rooted.